This invention relates to a simple vertical deflection circuit for a television apparatus.
In the field of surveillance and industrial cameras, it is desirable to keep the various circuits small in size, light in weight and relatively uncomplicated, with a low parts count, yet providing high quality operation. The vertical deflection drive for a small vidicon in a surveillance camera needs to supply only a relatively small amount of power. Thus, complex high-power drive circuits such as are commonly used in color television receivers are inappropriate. Nevertheless, size and centering controls are necessary.
A linear sawtooth generator and vertical deflection drive circuit are described in U.S. Pat. No. 3,646,393 issued Feb. 29, 1972 to Tarr. The Tarr arrangement provides independent size and centering controls, but has the disadvantages of requiring two separate amplifiers, one for deflection drive and the other for Miller integration, and has the further disadvantage of a sawtooth capacitor which is not coupled at either end to a fixed reference voltage. Such a floating sawtooth capacitor cannot be discharged by a switch driven relative to ground. Thus, the Tarr arrangement requires additional complexity in the circuits by which the sawtooth capacitor is driven. The Tarr arrangement includes a centering control which dissipates power continuously.
Simple sawtooth generators in which the capacitor is grounded are known, and the use of such sawtooth generators in conjunction with the vertical deflection circuit are also known, as described in U.S. Pat. No. 3,988,638 issued Oct. 26, 1976 to Nillesen. Such simple sawtooth generators, however, have the disadvantages of generating a nonlinear sawtooth voltage unless the source resistance is very high. An active current source could be used to linearize the charging current in an arrangement such as Nillesen's, but this introduces additional complexity.
It is desirable to have a vertical deflection circuit using resistor charging of a grounded sawtooth capacitor and which is provided with substantially noninteracting vertical size and centering controls.